1. Field of the Invention
The present invention is concerned with a procedure as well as a configuration in order to transmit data, especially data that is used in order to operate, monitor and control an external system.
It is possible to establish a data connection to a web server (WS) or Internet information server (IIS) from any computer through the WWW (World Wide Web), which is also known as the Internet. A WS or an IIS can be accessed via an Internet browser such as Microsoft's Internet Explorer or Netscape's browser.
While establishing a data connection from a web client a request is sent to an Internet server via the input of a URL address. If the connection works, the Internet server answers with an HTML site (HTML=hypertext markup language). WWW clients such as Netscape or the Internet Explorer communicate with the WWW server via the hypertext transport protocol (HTTP). Any data connection is thus based on a request protocol and, as a response to that, a response protocol.
2. Description of the Prior Art
Due to the limited capacities of transfer on the Internet and the wish to load more quickly, data structures on the Internet are built up efficiently. An average HTML site contains only few Kbytes; images are compressed with efficient algorithms, and applicative programs such as Java applets are interpreted by browsers. This relieves the source of the data in terms of storage capacity and CPU performance. Furthermore, operator control and monitoring surfaces can be easily created by means of web technology and popular software applications. Handling operator control and monitoring can be achieved with standard browsers whose use is generally known and whose interpretation can be grasped intuitively.
These features are required for the already very popular application of web server technology for the monitoring, controlling and remote maintenance of industrial systems and processes.
It is thus possible to access a remote web server of the system that needs to be operated/monitored via an Internet browser of a web client. The web server of the system can be accessed directly via a point-to-point connection (PP) or via the telephone by means of a modem. The web server can either be visible on the Internet directly via a hosting provider or it will be used within an Intranet or WANs.
The advantages of this application of web server technology for remote maintenance of systems via the Internet are obvious. For example, operator control and monitoring surfaces can be easily constructed by means of well-known Microsoft tools such as Word, Excel, PowerPoint and so on; they can be operated with user-friendly standard browsers Microsoft Internet Explorer and Netscape Communicator.
However, this well-known application of web server technology has one disadvantage when it comes to web servers which are visible on the Internet. The system that is monitored or controlled does usually not have permanent and transparent access to the Internet due to financial and security reasons.
Access to the Internet is now possible from any workplace via a modem or a dedicated line. However, the connection opened up by an Internet services provider (ISP) for a web browser has only very limited bi-directional usability. Therefore, company networks normally use an address that is not Internet-compatible. Internet access takes place via specifically configured proxy servers, routers, switches and firewalls. Additionally, Internet services providers (ISPs) have their own IP addresses. An address is assigned dynamically to each customer as soon as they access the Internet. Firewalls and proxy servers may be configured in some networks in such a way that they are capable of bi-directional data exchange; however, this kind of configuration is relatively complicated and often fails in practice due to lacking feasibility.